1. Field of the Invention
This invention relates to compositions curable by radical, cationic or radical/cationic polymerization initiated by light, electron beam or chemical initiators, and more particularly, to olefinically unsaturated polyester, styrene and vinylether formulations, and to their use for the production of coatings, patching or sealing compositions or for the production of neat or fiber-filled molded articles.
2. Description of the Prior Art
Formulations based on unsaturated polyesters (UPEs) containing styrene are used primarily in the manufacture of fiberglass-reinforced plastics (FRP) which find application in the construction, marine, and automotive industries. Non-fiber-filled UPE formulations are used to make gel-coats, automotive repair putty, synthetic marble, and UV curable coatings. Typically, unsaturated polyester resins (UPERs) are formulated with styrene as a comonomer which serves the dual purpose of lowering viscosity and acting as a crosslinking agent during cure. UPERs available in the market today usually contain between 30-50% styrene. However, an environmental issue facing such UPE manufacturers is the regulation of styrene emissions. Styrene has a relatively high volatility which results in its being released from both uncured resins at room temperature and at much higher rates during cure. The Environmental Protection Agency (EPA) included styrene in its Toxic Release Inventory (TRI) in 1987 and classifies it as a possible carcinogen. Organizations such as the Occupational Safety and Health Administration (OSHA) and the Clean Air Act Amendments (CAAA) have included styrene in a list of volatile organic compounds to which exposure should be limited. Accordingly, UPE manufacturers have considered using different monomers to replace styrene in applications that can result in considerable exposure to styrene monomer.
Vinylethers (VEs) are electron-rich monomers that can undergo rapid cationic homopolymerization as well as free-radical charge-transfer polymerization with electron deficient moieties such as maleates or fumarates present in typical UPEs. A majority of vinylethers are relatively safe to handle and are non-toxic alternatives to styrene. Vinylethers have attributes similar to styrene in terms of providing diluency and high reactivity with UPEs. Thus VEs may be used in conjunction with styrene to reduce emissions in applications where lowering of toxic emissions is desirable.
For example, vinylethers can be used with unsaturated polyesters to provide UV curable coatings. WO 90701512 describes UPE-VE coating formulations consisting of a 1:1 molar ratio of vinylether to UPE unsaturated groups which are cured using UV light and a suitable photoinitiator for use in metal coatings, dental products, glass laminates and stereolithography. Various vinylether monomers, both monofunctional as well as bifunctional, also have been mentioned as the VE component of such systems. Similarly, EP 0322808 A2 discloses liquid radiation curable compositions containing an unsaturated polyester component with compounds containing at least two vinylether groups.
WO 9748744 describes curable polyester compositions in which the polyester and/or comonomer is terminated with at least one bulky and/or hydrogen donating monofunctional alcohol.
U.S. Pat. No. 5,360,863 discloses the use of UPEs with vinylether and/or (meth)acryloyl groups as radiation curable or peroxide curable compositions for use as binders for coating, patching or sealing compositions and for the production of molded articles. Research Disclosure December 1994 Number 36846 disclosed a copolymer of VE with UPE in a 1:1 alternating structure. However, none of these references disclose, teach or suggest a system in which styrene (or its derivatives) is partially replaced by vinylethers as a comonomer to lower toxic emissions at a reasonable cost.